Well, the main reason why I bought a HX is because it is my daily driver, My EF9 with a 100 octane diet is expensive. So anyway I am concerned with adding a intake,header,exhaust on the HX lean-burn civic coupe. It is the same as the EX, except for the lean-burn air/fuel mapping. I know that in closed loop the ECU should compensate for the air/fuel ratio, but it can only handle so much. My other concern is when it is in open loop the ECU is running a mapped program, which possibly could be too lean. I know using premium fuel will help. I was just wanting to know if anyone else has experience with this system and adding intake/exhaust components. Any guesses, thoughts, and educated answers would be appriciated. Thanks

That would be correct, an ECU difference for the HX to EX. That would change all the anti-theft codes and so on. I don't have keyless/dealer alarm. So the only change with an EX ECU install would be the imoblizer key code system, and the factory stereo. The price will make you want to sit down too.